1. Technical Field
Embodiments of this disclosure relate to a droplet discharge head to discharge droplets, an image forming apparatus such as a printer, a fax machine, and a copier including the droplet discharge head, a polarization processing method of an electromechanical transducer, and a method of manufacturing the droplet discharge head.
2. Description of the Related Art
Generally, an inkjet recording apparatus including a droplet discharge head to discharge, for example, droplets of ink (hereinafter, referred to as ink droplets) is known as a printer, a fax machine, a copier, a plotter, or an image forming apparatus obtained by combining functions of these devices. In the inkjet recording apparatus, ink droplets are adhered to a sheet medium by a droplet discharge head while the medium is conveyed and an image is formed.
As the droplet discharge head, a configuration that includes nozzles to discharge droplets of a liquid such as the ink, a liquid chamber (also referred to as a pressure chamber, a pressurization chamber, and a discharge chamber) that communicates with the nozzles and stores the liquid, and a piezoelectric element functioning as an electromechanical transducer that pressurizes the liquid in the liquid chamber is known. In the droplet discharge head, if a voltage is applied to the piezoelectric element, vibration is generated to deform a diaphragm forming a part of a wall of the liquid chamber, the liquid in the liquid chamber is pressurized by the deformation of the diaphragm, and the droplets can be discharged from the nozzles. As the droplet discharge head, a droplet discharge head using a piezoelectric actuator of a flexure vibration mode of the piezoelectric element is put into practical use.
A piezoelectric element used for the piezoelectric actuator of the flexure vibration mode includes a first drive electrode, a piezoelectric layer, and a second drive electrode. The diaphragm and the piezoelectric element are formed as a laminate on a substrate forming the liquid chamber and an insulating film, wiring lines to electrically connect the first and second drive electrodes to the outside, and a terminal electrode are formed on the piezoelectric element. In addition, a holding substrate covering the piezoelectric element not to disturb displacement is bonded to a surface of the substrate provided with the piezoelectric element.
In crystal of the piezoelectric layer configuring the piezoelectric element, a polarization direction becomes random in a state immediately after the piezoelectric element is manufactured, as illustrated in FIG. 19A. Then, the voltage application is repeated, so that the crystal of the piezoelectric layer becomes an aggregation of domains in which polarization directions are aligned, as illustrated in FIG. 19B. The polarization direction of the crystal of the piezoelectric layer is preferably aligned when the droplet discharge head starts to be used, to stabilize a polarization characteristic of the piezoelectric element and a characteristic of the droplet discharge head using the piezoelectric element. Methods are proposed of executing polarization processing to align the polarization direction of the piezoelectric element before the droplet discharge head starts to be used.